Identify Dobereiner’s triads from the following groups of elements having similar chemical properties:

1. Mg (24.3), Ca (40.1), Sr (87.6)
→ \(24.3 + 87.6\over 2\) = \(111.9\over 2\)= 55.95 ≠ 40.01 ∴ Mg, Ca, Sr is not a Dobereiner’s Triad. 2 Marks
2. S (32.1), Se (79.0), Te (127.6)
→ \(32.1 + 127.6\over 2\) = \(159.7.9\over 2\)= 79.85 ≈ 79.0 ∴ S, Se, Te is a Dobereiner’s Triad. 2 Marks
3. Be (9.0), Mg (24.3), Ca (40.1)
→ \(9.0 + 40.1\over 2\) = \(49.1\over 2\)= 24.55 ≈ 24.3 ∴ Be, Mg, Ca is a Dobereiner’s Triad. 2 Marks

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